# Talk:Centre of the universe

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This is a question that often gets brought up so I decided to bash something out for it. ^{gnostic} 13:21, 7 November 2011 (UTC)

- Doesn't the universe need to be actually, really, genuinely, demonstrably infinite for this explanation to work?--Bob
^{Spring is sprung!}16:43, 7 November 2011 (UTC)- No, just lacking in boundaries. For example, in the context of
*only*the two dimensional surface of the Earth (which is finite) where is its centre?^{pathetic}17:03, 7 November 2011 (UTC)- OK. So what is the difference between unbounded three dimensional space and infinite three dimensional space?--Bob
^{Spring is sprung!}17:09, 7 November 2011 (UTC)- The universe is warped so that it's finite but boundless - analogous to the surface of a sphere. The fact that it has three dimensions doesn't make this particularly impossible, but it does make it somewhat difficult to visualise.
^{gnostic}17:19, 7 November 2011 (UTC)- I'm still a bit unclear on boundless but not infinite. If something is infinite in extent it is presumably also boundless. I sorta feel that the inverse is true - the the boundless is also infinite. But as I'm a little unclear on what exactly you are using "boundless" to mean I could be wrong on this one.
- I'm pushing this point because the tone of the article seems to be suggesting that the concept is easy to grasp or that only the hard of thinking will have problems. Examples are:
- The idea that the universe has a centre still baffles creationists and a few people such as flat Earth or fixed Earth advocates, who think that there must be some centre to the universe.
- You don't need to have qualifications in general relativity to conclude that the universe has no centre.

- Maybe we should acknowledge that it's a difficult thing to get your brain around?--Bob
^{Spring is sprung!}19:42, 7 November 2011 (UTC)- Something infinite in extent is also boundless, that much is true. But there's a difference between infinite (and boundless by definition) and finite and boundless. The lack of a boundary
*only*doesn't help clear up the difference - which is where the cosmology gets a bit more esoteric and difficult. But let's look at the difference. The surface area of the Earth is 510,072,000 km^{2}. This is*finite*. We can count up to that number but we only have so much surface area on our sphere to work with. But, compare to, say, the Discworld there isn't a boundary on the 2-dimensional surface of the Earth. You can fall off the Rim on Discworld, but you cannot reach the edge of the Earth, or fall off this edge - the edge doesn't exist. Instead, if you keep walking, you come back to the same point you started on eventually. Say, you took off from Quito, Ecuador (because Google tells me the airport is very close to the equator) and flew west. You could cover a finite amount of ground but eventually could land in Quito, Ecuador again. And you could do it again, at no point, no matter what turns you took would you run out of land or hit an edge. But the Earth's surface, despite this, is still the finite 510,072,000 km^{2}it was before. We can visualise this fine, because we're 3-dimensional creatures who can perceive that the Earth is a sphere, visualising this same thing in 4-dimensions is hard, if not impossible. - But we can get the idea of what we're dealing with (and why it's hard to imagine) by going into a lower dimensional system. Imagine that we weren't, as such, able to perceive the curve of the Earth, either we were too small, the Earth too big, or we simply didn't have that knowledge (perhaps we're actually the inhabitants of Flatland). We would think that we were confined to just this 2-dimensional space that would presumably go on forever.
, we set off walking one day, leaving a marker to show our starting point, and then after a while we come back to that point again. We wonder "what the holy fuck?" because it seems impossible. The world is just 2-dimensional, how can we have done this trick? Remembering, that in Flatland we're not aware of this third dimension**But***at all*and cannot conceive it. Then some clever dick comes along as says "aha, but we're actually wrapped around another dimension" - "poppycock!" cry the inhabitants of Flatland "we can't conceive of this dimension". You cannot accurately portray a 3D object in 2D - at best you can do shadows, projections and poor representations, much like how we can't accurately show a hypercube on a computer monitor (not only does one face tend to remain hidden in our projection, but we're also incapable of constructing the object in our heads where*all*the angles are truly 90 degrees). Of course, back in reality we*can*conceive this third dimension that Flatland wraps around because we're 3D beings, and can view the Flatlanders as just victims of their limited vision. To us, in 3-D it's obvious that a 2-D plane can warp around, as easily as rolling up a newspaper. Now we need to think about how 3-D space can warp around another additional dimension. Suddenly, we realise that we too are Flatlanders not even able to conceive of the fact that our 3-D space can wrap around a fourth dimension. - While this model of the universe is all a consequence of higher level physics and general relativity, I don't think the concept requires it. The universe is either two things; infinite, or finite. If it's infinite in extent, then we can
*literally*travel forever and never come back to where we started - like a free-roaming computer game that procedurally generates new landscapes to explore, there is no boundary to the world and always new places to travel to. We can conclude that there is no centre that is non-arbitrary because there is no boundary and extent is infinite. But what if the universe was finite? Then there's only*so much*space that we can utilise to build our universe, much like the limited 510,072,000 km^{2}of the Earth's surface. We then are faced with two further possibilities; does the universe have a boundary, or not. If it does have a boundary, then it further raises the complex question; where is it, and what's beyond it. A boundary to the universe implies some kind of brick wall that we could come up against that marks the edge. We could run headlong into this boundary and break through it, or we could bounce off it - this is an absurd notion because in order for either of these properties to apply to the boundary, the boundary must be part of space and time. So there must be a boundary beyond*that*boundary to stop us moving out (containing the first boundary) but that too must be part of space and time to contain the second boundary and stop us passing it... beyond that a third, fourth and so on and suddenly we're back at the infinite universe again - all of which is still composed of "all of space and all of time" even though most of it seems to be built of metaphysical brick wall. We define the universe as everything, "all space and all time" - space and time began at the big bang, and asking what came before is like asking "what is north of the north pole". So if there is something beyond it, then it cannot be the*entire*universe. What is beyond this boundary must be part of the universe too, and what is beyond the boundary of that must also be part of it - and we come back to the first point about it being infinite. You can plead about heaven and alternate dimensions and supernatural realms but even assuming these it does not alter the definition of the universe being "all of space and all of time" - if it's an alternate universe, or heaven or any other place like that lies beyond the hypothetical boundary then these would be classes as*part of*"all of space and all of time" and*not*the supernatural nether-realms that they were originally proposed as. - So the universe cannot be bounded by definition - there's simply nothing for it to be bounded
*by*. So this leaves two options; infinite in extent so that there is an unlimited amount of space to explore, or finite in extent but boundless so that there is only so much space to explore but no boundary to hit to say when we can stop. From our perspective, the difference between these two models is subtle and perhaps almost nonsensical, and this is where higher level cosmology and the various hypotheses about the multiverse comes into play. But that's a different story entirely. The point is that by definition, the universe is either infinite in extent, or finite but boundless, and both of these options preclude the prospect of a centre. - Interestingly, it does preclude other attributes. For instance, the universe cannot spin - because it can't have anything to spin
*relative to*. Similarly it can't really move, as such, because it has nothing to move around in. **Tl;dr version;**perhaps it isn't too simple, but we can explain it without a single field equation, so that's a good sign, right?^{sshole}14:49, 8 November 2011 (UTC)- You know, if I added 400 more words to that it would be my daily quota of NaNoWriMo writing!
^{sshole}14:52, 8 November 2011 (UTC)- I understand the 2D issue quite well. But it's an argument by analogy which - as far as I can see - makes it's next two points by simple assertion.
- That there is an analogous situation in 3D space and,
- that the universe is an example of such a situation.

- It's a good way of thinking about the issue once it has been accepted, but it's not by itself evidence that the hypothesis is correct.
- It is possible, indeed probable, that there a mathematical explanation for this and that it does not lend itself well to text. But this is my point - the article is written in such a way that it implies that only an idiot would have problems understanding it. I disagree - I think it's tough and complex.--Bob
^{Spring is sprung!}15:42, 8 November 2011 (UTC)- Yeah, it probably is a bit on the complex side. It's certainly conceptually impossible. Spacetime is all represented in mathematics and geodesic manifolds and things like that. Then there's local and global geometries and well, there are a few other explanations. The above one is the simplest based on some of Hawking's analogies.
^{gnostic}15:57, 8 November 2011 (UTC)- There's also the "Doughnut theory of the universe".
^{moral}16:00, 8 November 2011 (UTC)

- There's also the "Doughnut theory of the universe".

- Yeah, it probably is a bit on the complex side. It's certainly conceptually impossible. Spacetime is all represented in mathematics and geodesic manifolds and things like that. Then there's local and global geometries and well, there are a few other explanations. The above one is the simplest based on some of Hawking's analogies.

- I understand the 2D issue quite well. But it's an argument by analogy which - as far as I can see - makes it's next two points by simple assertion.

- You know, if I added 400 more words to that it would be my daily quota of NaNoWriMo writing!

- Something infinite in extent is also boundless, that much is true. But there's a difference between infinite (and boundless by definition) and finite and boundless. The lack of a boundary

- The universe is warped so that it's finite but boundless - analogous to the surface of a sphere. The fact that it has three dimensions doesn't make this particularly impossible, but it does make it somewhat difficult to visualise.

- OK. So what is the difference between unbounded three dimensional space and infinite three dimensional space?--Bob

- No, just lacking in boundaries. For example, in the context of

- You could always link to QI. Dr. Cox (you said cox, hehehe...heheh...heheh) explained how there is no center or beginning point, and equally that EVERYTHING is the center and beginning point. I nodded, knowingly. Cause of course both not having a center and all being a center is just sooooo damned easy to understand, non? (damned physics, anyhow.)GodotGet over it!. 20:16, 7 November 2011 (UTC)